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(20) variable zener - 2½ to 36 v (or simple audio amp)
TL431c ZENER / Shunt Regulator
Qty (20) - from Texas Instruments (TI)
"The Adjustable Zener" (or even a 400 mW Audio Amplifier)
Experimenters absolutely this simple but versatile programmable shunt voltage regulator. A single TL431 and a small trimmer potentiometer will replace a whole assortment of zeners. Better yet, since the reference voltage is continuously adjustable from 2 to 36 VDC, you will do it with better precision.
Never settle for a 'close' fixed zener value again. Afterall, what good is a 1% zener, if it's nominal voltage is 3% off your target voltage?
Setting the voltage is very easy. Simple algebra is used for the various configurations listed in the datasheet.
This device works as a current shunt, just like a zener. It will sink 1 to 100 mA to maintain a precise Positive or Negative voltage from 2 to 36 VDC. All you need is the series current limiting resistor (as with zeners) and a voltage divider consisting of two small resistors (R1/R2) to program the voltage.
* Replace R1/R2 with a trimmer for a precision adjustable zener diode.
* Add a 'pass' transistor for higher load currents.
* Need an adjustable, constant current source/sink? This device can do that too, very easily.
Datasheet - TI TL431 (572K PDF)
Need a simple AUDIO AMPLIFIER? See the 2 examples below.
Check the TL431 datasheet. It has many applications to spur your imagination. This 'zener' can even be used as a microphone / phono amplifier (left) or as a Crystal Radio amplifier using a 32 Ohm speaker without a transformer!
Popular TO-92 3-terminal package. Only 3 resistors (not included) are needed to make a precision regulated voltage source. The perfect replacement for even tight tolerance zener diodes.
